CN1529757A

CN1529757A - Fusion Protein for secretion of protein of interest in supernatant of bacterial culture

Info

Publication number: CN1529757A
Application number: CNA028068505A
Authority: CN
Inventors: P; P·哈伯曼; ض�; J·埃特尔
Original assignee: Aventis Pharma Deutschland GmbH
Current assignee: Sanofi Aventis Deutschland GmbH; Wacker Chemie AG
Priority date: 2001-02-20
Filing date: 2002-02-08
Publication date: 2004-09-15
Anticipated expiration: 2022-02-08
Also published as: JP4243104B2; NO20033673D0; WO2002068660A1; PE20020876A1; ZA200305869B; ES2254658T3; ATE314480T1; DE10108212A1; DE60208343D1; KR20030074842A; DE60208343T2; CA2438886A1; BR0207394A; IL157414A0; NO20033673L; HK1065335A1; CN100500853C; AU2002231784B2; JP2004518444A; NO331271B1

Abstract

The invention relates to fusion proteins comprising a fusion part and a protein of interest, the combination of the two proteins leading to the fusion protein being secreted into the supernatant of a bacterial host and the protein of interest being present in its correct three-dimensional structure.

Description

Fusion protein for secreting a protein of interest in the supernatant of a bacterial culture

Description of the invention

The present invention relates to fusion proteins comprising a protein of interest and a fusion moiety, the combination of the two proteins resulting in secretion of the fusion protein into the bacterial host supernatant, and the protein of interest being present in the correct three-dimensional structure. The gene sequence of the fusion protein is part of an expression cassette that can be expressed in a bacterial host. The present invention relates to a method for fermentation, expression and post-treatment of the fusion protein using the expression cassette; to plasmids containing such expression cassettes; to bacterial host cells containing such expression cassettes integrated into the chromosome and/or as replicons (e.g. as plasmids); to said fusion protein with hirudin or a derivative thereof as fusion moiety; to a method for producing insulin or an insulin derivative; and to the use of said expression cassette in a process for the preparation of a fusion protein from hirudin or a derivative thereof and for the production of insulin or an insulin derivative.

The development of an optimized process for the production of a drug based on a recombinant protein should meet the following two points as far as possible, firstly, the process should be as cost-effective as possible and secondly, the product should reach the highest purity.

In this regard, the choice of expression system determines the course of a particular production method, and as will be apparent to the skilled person, the development of new protein-chemical techniques, the possibility of a variety of biochemistries, and new combinations of known techniques will always make possible the improvement of existing methods.

The choice of host cell system for synthesis is determined by the properties of the desired protein. Bacteria such as E.coli represent a system with which crude yields of several grams of protein can be produced rapidly in inexpensive media. The system is particularly useful for proteins that do not require modification and that can be renatured in vitro to their biologically active form. For large amounts of a desired protein (such as insulin), it is intended to obtain an expression rate that results in the accumulation of the protein in the form of inclusion bodies within the cell. After cell lysis, the protein is solubilized and allowed to fold in further method steps thereafter. However, the folding process is not quantitative. This may be due to irreversible damage during inclusion body formation, corresponding damage upon cell lysis, and errors during folding. Subsequently, the "misfolded or modified molecules have to be removed in a further separation step. This is disadvantageous in saving production costs. In addition, traces of the molecule may also reappear in the final product. Due to the high purity standards that the drug substance is to meet, a reasonably careful and costly purification is required. Due to the favourable cost/crude yield ratio, a method for secreting the correctly folded form of the protein of interest from E.coli into the culture medium would be desirable. However, this has been successful in some special cases to date.

This particular case is described in International patent application PCT/EP 00/08537. When a specific secretion signal sequence was used, Klevel lepirudin (drug Refludan) was successfully synthesized and secreted using Escherichia coli^Active ingredient of (a). German patent application No. 10033195.2 (unpublished) describes a bifunctional protein comprising hirudin and hirudin derivatives and factor Xa inhibitors and derivatives thereof from ticks. The protein can also be synthesized and secreted in large quantities using E.coli. In addition to this finding, it was subsequently surprisingly found that hirudins can be secreted not only in large amounts in the form of TAP fusion proteins, but also as part of fusion proteins with polypeptides, such as proinsulin derivatives; it has also been found to be biologically active and surprisingly, the fusion moiety such as proinsulin is present in the correct three-dimensional structure. This unexpected result makes it possible to produce e.g. insulin in a more cost-effective way using a bacterial host/vector system, since the step of in vitro folding after intracellular expression, which may result in a non-negligible yield loss, and the resulting simpler protein purification process, can be dispensed with. Another advantage is that no chaotropic auxiliary agents are required for dissolving the fusion protein, which is necessary when using E.coli for insulin production in conventional methods. Ecologically, this leads to less environmental pollution by avoiding the corresponding waste.

Leeches of the leech species (Hirudo) have formed, for example, a number of isoforms of the thrombin inhibitor hirudin. Hirudins have been optimized to the pharmaceutical requirements by artificial variation of the molecule (e.g.by alteration of the N-terminal amino acid) (see EP-A0324712).

The invention encompasses the use of hirudin and hirudin variants in the formation of fusion proteins, for example with simian proinsulin or derivatives thereof. A particular embodiment of the invention uses one of the natural hirudin isoforms (all natural hirudin isoforms are collectively referred to as "hirudin"). Natural isoforms are, for example, Val-Val-hirudin or Ile-Thr-hirudin. Other embodiments of the invention use variants of the natural hirudin isoforms. Variants are derived from the natural hirudin isoforms, but contain, for example, amino acid additions and/or amino acid deletions and/or amino acid alterations compared to the natural isoforms. The hirudin variants may contain alternating peptide fragments of the natural hirudin isoforms and new amino acids. Hirudin variants are known and described, for example, in DE 3430556. Hirudin variants are commercially available in the form of proteins (Calbiochem)^Biochemicals, catalog numbers 377- > 853- > 950- > 960).

Insulin is a polypeptide having 51 amino acids distributed over two chains of amino acids: a21 amino acid a chain and a 30 amino acid B chain. The two chains are connected to each other by 2 disulfide bridges. Insulin compositions have been used for the treatment of diabetes for many years. This includes not only the use of natural insulin but also the use of insulin derivatives and analogues.

An insulin derivative is a derivative of a natural insulin, i.e. human or animal insulin, which differs from the corresponding natural insulin by substitution of at least one natural amino acid residue and/or addition of at least one amino acid residue and/or an organic residue, otherwise the insulin derivative is identical to the natural insulin. In general, insulin derivatives have slightly different effects compared to human insulin.

Insulin derivatives with accelerated onset of action are described in EP 0214826, EP 0375437 and EP 0678522. EP 0214826 et al relates to the replacement of B27 and B28. EP 0678522 describes insulin derivatives with different amino acids (preferably proline, but not glutamic acid) at position B29. EP 0375437 relates to insulin derivatives with lysine or arginine at position B28, which may, if desired, be additionally modified at B3 and/or a 21.

EP 0419504 discloses insulin derivatives which are resistant to chemical modification by modification of asparagine at B3 and at least one other amino acid at position a5, a15, a18 or a 21.

WO 92/00321 describes insulin derivatives in which at least one amino acid in positions B1-B6 is replaced by lysine or arginine. According to WO 92/00321, this insulin exhibits a prolonged action.

When producing insulin and insulin derivatives using genetic engineering, an insulin precursor, i.e. "proinsulin", is often expressed which comprises B, C and the a chain. The proinsulin can be converted into insulin or insulin derivatives by enzymatic or chemical removal of the C chain after appropriate and correct folding and formation of disulfide bridges. Proinsulin is often expressed as a fusion protein. The "unwanted" fusion moiety also requires chemical or enzymatic removal.

It will be apparent to those skilled in the art that the methods of culturing, propagation and fermentation of the recombinant cells will depend on the recombinant host/vector system chosen. This is also the subject of the invention.

This fusion protein shows surprisingly good solubility in acidic medium, which leads to a unique advantage in the chemical post-treatment of this protein. Firstly, many of the undesired components of the supernatant can be precipitated under the conditions described, and secondly the peptidases or proteases are inactivated under the conditions described. Thus, at the end of the operation, acidification of the fermentation broth will make it possible to separate the unwanted supernatant protein together with the host cells directly from the fusion protein and to concentrate the fusion protein in a further step. This is also the subject of the invention.

At the end of the fermentation, the folding process may not be 100% complete. The addition of a thiol or, for example, cysteine hydrochloride, can complete the process. This is also the subject of the invention.

If the two proteins are fused via an amino acid linker specifically recognized by an endoprotease that effectively cleaves the fusion protein only at the amino acid linker and not at other positions, the protein of interest can be cleaved directly in active form. In the production of insulin, the linker between hirudin and proinsulin preferably contains an arginine at its carboxy terminus. This allows the use of trypsin conversion in a simultaneous process to cleave the fusion moiety and convert proinsulin to mono-or di-Arg-insulin. The linker must be optimized with respect to the insulin processing such that the cleavage of the hirudin part is not slower than the cleavage of the C peptide sequence or its derivatives connecting the insulin B and A chains. This is also the subject of the invention. An example of an expression system that can be used is the vector pJF118, which is described in figure 1 of european patent 0468539.

Plasmids containing DNA sequences which code for proinsulin or proinsulin derivatives are described, for example, in patents EP-A0489780 and PCT/EP 00/08537.

Plasmid pK152 (according to EP-A0324712) containing a hirudin sequence was used as a source of the hirudin DNA sequence.

Compatibility of export of the protein of interest with respect to crossing the bacterial inner membrane is very important for secretion. In this connection, it is important to select a signal sequence which is more or less optimal for different proteins, and patent application PCT/EP00/08537 describes a PCR-based signal sequence screening system. Since the hirudin activity surprisingly remains intact and can thus be easily detected in the supernatant by a thrombin inhibition assay, this system can also be applied to fusion proteins having hirudin as the N-terminal fusion moiety.

The invention thus relates to DNA (alternative term: expression cassette) which codes for a fused white matter and which has-F-As_m-R_n-a form of-Y-wherein,

wherein

F is a DNA sequence encoding an amino acid sequence which allows secretion of the protein Y into the fermentation medium,

as is a chemical bond or a DNA sequence encoding an amino acid that can be encoded by the genetic code,

m is an integer of 0 to 10

R is a chemical bond or an arginine codon,

n is 0 or 1, and

y is a DNA sequence coding for a protein of interest which is correctly folded in the fermentation medium and is part of a fusion protein,

in which in particular DNA sequences are selected which code for hirudin or a derivative thereof (F) and proinsulin or a derivative thereof (Y).

The invention also relates to P-S-F-As_m-R_nAn expression cassette of the form Y-T (alternative term: DNA molecule),

wherein

P is a promoter, and the promoter is a promoter,

s is a DNA sequence encoding a signal sequence which leads to an optimal yield,

t is an untranslated DNA sequence which can enhance expression.

The invention also relates to plasmids containing the above-mentioned expression cassettes, and also to host cells containing said plasmids, or preferably containing the expression cassettes integrated into the host genome, selected from the group consisting of E.coli, B.subtilis and Streptomyces (Streptomyces).

The invention also relates to a method for the fermentative production of the above-mentioned fusion proteins, in which method

(a) The DNA molecule as described above is expressed in a host cell as described above, and

(b) isolating the expressed fusion protein;

in particular, in the method, the supernatant is separated from the host cell to isolate the expressed protein, and then the expressed protein is separated from the supernatant; in the method, the step for concentrating the expressed protein in the supernatant after precipitation is selected from the group consisting of microfiltration, hydrophobic interaction chromatography and ion exchange chromatography; in a particular embodiment of the method, isolating the expressed protein comprises the step of precipitating components in the culture medium or supernatant to keep the expressed protein in solution; in another preferred embodiment of the process according to the invention, after fermentation, the addition of thiol or cysteine hydrochloride to the fermentation supernatant at a pH of 6 to 9 results in a free SH group concentration of 0.05 to 2.5 mM.

A particular embodiment of the invention comprises isolating the fermentation supernatant from the host cell, further culturing the host cell in fresh medium and isolating the released fusion protein from the supernatant. In other words, another embodiment of the present invention is a method as described above, in which, after separation of the fermentation supernatant from the host cells, the host cells are repeatedly cultured in a fresh medium, and the released fusion protein is isolated from each supernatant obtained during the culture.

The invention also relates to a method for producing insulin or an insulin derivative, in which method,

(a) from the expressed protein obtained by the method described above

(b) Releasing the protein of interest, in particular insulin or an insulin derivative, by enzymatic or chemical cleavage, and

(C) isolating the protein of interest.

The following examples are intended to describe the invention in more detail without intending to limit the invention.

Example 1: construction of lepirudin-GNSAR-simian proinsulin fusion protein following addition to the Signal sequence from the Pseudomonas fluorescens oprF Gene product

Patent application PCT/EP00/08537 example 2 describes an expression vector for E.coli which enables the expression and secretion of Refludan into the culture medium via the signal sequence of the P.fluorescens oprF gene product (De, E. et al, FEMS microbiology letters, 127, 263-272, 1995). This vector was used to construct Refludan-gnars-simian proinsulin fusion protein (gnars ═ SEQ ID No.: 1), and was defined as pBpfu _ hir.

Additional starting materials were pJF118(EP 0468539) and pK152(PCT/EP00/08537) plasmid DNA. The following oligonucleotides are necessary:

primer pfuf1

5′GGTTCTCTTA TTGCCGCTAC TTCTTTCGGC GTTCTGGCAc ttacgtatac tgactgca

3′

(SEQ ID NO.：2)

Primer insu11HindIII

5′-TTTTT AAGCT TCATGTTTGA CAGCTTATCA T-3′(SEQ ID NO.：3)

Primer Hir _ insf1

5′ATCCCTGAGG AATACCTTCA GGGAAATTCG GCACGATTTG TG-3′(SEQ IDNO.：4)

Primer Hir _ instrev 1

5′-CACAAATCGT GCCGAATTTC CCTGAAGGTA TTCCTCAGGG AT-3′(SEQ IDNO.：5)

Primer pfuf1 hybridizes to a region of the DNA encoding the junction of the signal sequence and lepirudin on the expression vector.

The part shown in bold in the primer Hir _ instrev 1 hybridises with the DNA region encoding the junction of the preproinsulin and simian proinsulin sequences on the plasmid pINT90d and with the 3' end sequence of the hirudin sequence on plasmid pK 152. Primer Hir _ instrev 1 is 1100% complementary to primer Hir _ inst.

Primer insu11HindIII marks the 3' end of the DNA region cloned in pINT90d and encoding the simian proinsulin sequence and additionally carries a hexanucleotide sequence recognized by the restriction enzyme HindIII.

Two standard polymerase chain reactions were performed using the Hir _ insf1/Insu11hindIII primer pair and plasmid pINT90d as templates and pfuf1/Hir _ instrev primer pair and plasmid pBpfu _ Hir as templates. The two reaction products were mixed and an aliquot was removed for a third polymerase chain reaction using the primers pfuf1/Insu11 HindIII. The result is a DNA product containing the signal (part) -lepirudin-GNSAR-simian proinsulin sequence. The DNA fragment was digested with the restriction enzymes BamH I and HindIII, which BamH I is in the lepirudin sequence and HindIII is cut at the 3' end of the proinsulin coding sequence.

In a parallel reaction, the vector pBpfu was digested with the two enzymes and the large vector fragment was isolated. The isolated products of the two reactions were ligated in a T4 ligase reaction. Coli strain K12 Mc1061 competent cells (Sambrook et al, molecular cloning (Cold Spring harbor Laboratory Press)1989) were transformed with the ligation mixture and plated onto NA plates containing 25. mu.g/ml ampicillin. Plasmid DNA was isolated from the transformants for identification. At the same time, transformants identified by plasmid analysis were plated for seed conservation. DNA was identified by restriction analysis and DNA sequence analysis. The plasmid identified as correct was designated pBpfuHir _ Ins.

Example 2: construction of a Ser-hirudin-GNSAR-simian proinsulin fusion protein appended to the outer membrane protein (fimD) Signal sequence of Salmonella typhimurium (S.typhimurium)

The construction was carried out according to the protocol described in example 1.

Patent application PCT/EP00/08537 example 10 describes the construction of vectors for export of lepirudin via the Salmonella typhimurium outer membrane protein signal sequence (Rioux, C.R., Friedrich, M.J., and Kadner, R.J.; J.Bacteriol.)172(11), 6217-6222 (1990)). The resulting plasmid was designated pBstyfim _ hir for experimental purposes. The DNA of plasmids pK152 and pINT90d served as templates in each case.

Construction required 4 primers.

Primers insu11HindIII, Hir _ insf1 and Hir _ instrev 1 were as described in example 1.

Primer styfimf1 was newly synthesized and its sequence was as follows:

5′CGGCGCTGAG TCTCGCCTTA TTTTCTCACC TATCTTTTGC CTCTacgtat

actgactgcaCTG 3′(SEQ ID NO.：6)

the DNA triplets shown in bold represent serine codons. This results in the production of hirudins with a serine in place of a leucine in position 1 of the amino acid sequence.

Similar to example 1, two standard polymerase chain reactions were carried out using the Hir _ insf1/Insu11HindIII primer pair and plasmid pINT90d as templates and styfimf1ser/Hir _ instrev primer pair and pK152 DNA as templates. The two reaction products were mixed and an aliquot was removed for a third polymerase chain reaction using the primer styfimf1ser/Insu11 HindIII. The result is a DNA product which contains the signal (part) -Ser-hirudin-GNSAR-simian proinsulin sequence. The DNA fragment was digested with restriction enzymes BamH I and HindIII.

In a parallel reaction, the vector pBstyfim _ Hir was digested with the two enzymes and the large vector fragment was isolated. The isolated products of the two reactions were ligated in a T4 ligase reaction. Coli strain K12 Mc1061 competent cells were transformed with the ligation mixture. Plasmid DNA was isolated from the transformants for identification. At the same time, transformants identified by plasmid analysis were plated for seed conservation. DNA was identified by restriction analysis and DNA sequence analysis. The plasmid identified as correct was designated pBstyfim _ SerHir _ Ins.

Example 3: construction of Ala-hirudin-R-simian proinsulin fusion protein appended to the Signal sequence of the E.coli alkaline phosphatase precursor protein

The E.coli alkaline phosphatase precursor protein has the signal sequence:

MKQSTIALAL LPLLFTPVTK A(SEQ ID NO.：7)

(Shuttleworth H.，Taylor J.，Minton N.；Nucleic Acids Res.14：8689，(1986)).

this peptide sequence was translated into DNA by the GCG program Backtranslate (Wisconsin Package version 10.1, Genetics Computer Group (GCG), Madison, Wisc.) using the E.coli high codon usage standard.

This results in the following sequence:

5′ATGAAACAGTCGACCATCGCGCTGGCGCTGCTGCCGCTGCTGTTCACCCCGGT

TACCAAAGCG 3′(SEQ ID NO.：8)

to clone and add this sequence to a DNA sequence encoding hirudin, characterized by an alanine in position 1 (EP-A0448093), the sequence is extended by the following sequence shown in bold:

5′TTTTTTGAATTCATGAAACAGTCGACCATCGCGCTGGCGCTGCTGCCGCTGCTGTTCAC

CCCGGTTACCAAAG-CG GCTacgtat actgactgcaCTG(SEQ ID NO.：9)

the following partially overlapping two oligonucleotide sequences are derived therefrom.

The primer phoaf1 has the following sequence:

5′CTGCTGCCGCTGCTGTTCACCCCGGTTACCAAAGCG GCTACG

TATACTGACTGCACTG-3′(SEQ ID NO.：10)

the primer phoaf2 has the following sequence:

5′TTTTTTGAATTCATGAAACAGTCGACCATCGCGCTGGCGCTGCTGCCGCTGCTG-3′(SEQ ID NO.：11)

the construction of the expression vector requires the DNA of the primers insu11HindIII, Hir _ insf2 and Hir _ instrev 2 and the plasmids pK152, pINT90d and pJF 118.

The primer Hir _ insf2 has the following sequence:

5′-ATCCCTGAGGAATACCTTCAG cgaTTTGTGAACCAGCAC C -3′(SEQ ID NO.12)

the primer Hir _ instrev 2 has the following sequence:

5′-GGTGCTGGTTCACAAA tcgCTGAAGGTA TTCCTCAGGG AT-3′(SEQ ID NO.13)

the capital letters in bold indicate sequences which hybridize to proinsulin, while the capital letters in common indicate sequences which overlap the 3' end of the hirudin sequence. Underlined lower case letters indicate codons for linker arginine.

In analogy to example 1, two standard polymerase chain reactions were carried out using the Hir _ insf1/Insu11HindIII primer pair and the DNA of the plasmid pINT90d as templates and the phoaf1/Hir _ instev primer pair and the pK152 DNA as templates. The products of the two reactions were mixed and an aliquot was removed for a third polymerase chain reaction using the primers phoaf1/Insu11 HindIII. The result is a DNA product containing the signal-Ala-hirudin-GNSAR-simian proinsulin sequence. The DNA fragment was digested with restriction enzymes BamH I and HindIII. In a parallel reaction, the vector pJF118 was digested with the two enzymes and the large vector fragments were isolated. The isolated products of the two reactions were ligated in a T4 ligase reaction. Coli strain K12 Mc1061 competent cells were transformed with the ligation mixture. And plasmid DNA was isolated from the transformant for identification. At the same time, transformants identified by plasmid analysis were plated for seed conservation. DNA was identified by restriction analysis and DNA sequence analysis. The plasmid identified as correct was designated pNS 22.

Example 4: thrombin inhibition assay

The hirudin concentration is determined by the method of Grie β bach et al (ThrombosisResearch)37, p.347-350, 1985). To this end, a specific amount of a Refludan standard is included in the assay to establish a calibration curve from which the amount of product (mg/l) can be directly determined. Biological activity is also a direct measure of the correct folding of the proinsulin component of the fusion protein. Alternatively, S.aureus (S.aureus) proteolytic digestion and subsequent analysis by an RP-HPLC system can be used to determine correct S-S bridge formation.

Example 5: expression of fusion proteins

The recombinant cells were cultured overnight in 2YT medium (per liter: 16 g tryptone, 10 g yeast extract, 5 g NaCl) containing 100. mu.g/ml ampicillin. The overnight culture was diluted 1: 50 with fresh medium and the cells were cultured to a density of about 0.8OD₆₀₀。

Expression was then induced by adding IPTG to 0.05-2 mM. Cells induced in this manner were further incubated for 3-26 hours.

After 3 hours, the antithrombin effect of hirudin in the supernatant was clearly measured. Since SDS PAGE after Coomassie blue staining showed only new bands in induced cells that reacted with polyclonal anti-insulin antibodies in Western blot analysis, the effect was attributed to secretion of the fusion protein of interest. In fermentation experiments, induction only started when cultured to significantly high optical densities. Synthetic media based on minimal media are preferred here.

Cell productivity can be increased by using the principle of drawing bacterial "milk" (i.e. by carefully removing the cells from the supernatant and further incubating the cells in fresh medium after an optimal induction time, and then the inducer can be added again to the medium. Insulin was then prepared in parallel from the harvested supernatants.

Example 6: purification of fusion proteins

After induction, the cell supernatant is adjusted to pH2.5-3 and the cell and supernatant components are removed by centrifugation or filtration. The supernatant after precipitation was applied to a cation exchange column (S-Hyper DF, Source 30S) and fractionated using a 150 to 450mM NaCl linear gradient at pH 3.5 in the presence of 30% 2-propanol. Fractions were analyzed by RP-HPLC method. The proinsulin-hirudin fusion protein elutes at a NaCl concentration of about 300 mM. Sufficiently pure fractions were combined, diluted with 0.1% TFA and applied to an RP column (PLRP-S7.5X 50mm) using a pump. Elution was performed with a gradient of 25-50% acetonitrile. The two fractions were combined. The material was lyophilized after removal of the solvent. The purity of the material was checked by SDS polyacrylamide electrophoresis. The purified fusion protein was analyzed by mass spectrometry (ESI). The molecular weight of the fusion protein determined experimentally corresponded to its theoretically expected molecular weight after removal of the signal peptide.

Example 7: determination of disulfide bridge connection

The fusion protein was digested with trypsin and the fragments formed were analyzed by RP-HPLC method and subsequently by mass spectrometry. The fragment identified as de- (B30) insulin was successfully identified based on its mass of 5706 Da. This product was digested with staphylococcus aureus (s. aureus) V8 protease. RP-HPLC analysis showed the expected peptide profile.

Trypsin cleavage was performed as follows:

the lyophilized fusion protein was dissolved in 50mM Tris-HCl pH 8(1mg/ml) and trypsin (1. mu.g per mg of fusion protein) was added. After the reaction was completed, the pH was adjusted to 3 to inactivate trypsin.

Staphylococcus aureus (s.aureus) digestion was performed as follows:

the isolated de- (B30) insulin was dissolved in water at pH 8 and staphylococcus aureus (s. aureus) protease (1/50 in terms of insulin amount) was added. And the mixture was incubated at 37 ℃ for 5 hours and then at room temperature overnight.

Example 8: purification of insulin

Unlike most other polypeptides present in the supernatant, which are either due to spontaneous lysis of the host cell or due to secretion, fusion proteins surprisingly do not precipitate at pH 2.5-3.5. The medium can thus be suitably acidified and subsequently after the precipitation has been completed the precipitate and the cells are removed by centrifugation or microfiltration and concentrated.

Subsequently, the medium was adjusted to pH 6.8 and the fusion protein content was determined in parallel by analytical HPLC assay. After the measurement, trypsin was added to the supernatant to make it about 1. mu.g per 1-1.5mg of the fusion protein. After incubation at room temperature for about 4 hours, purification was performed using a cation exchange resin in the presence of 2-propanol at pH 3.5. Elution was performed by applying a gradient of 0.15 to 0.45M in buffer.

bis-Arg-insulin elutes at about 0.3M. After 1: 1 dilution, bis-Arg-insulin was purified by addition of 10% strength ZnCl₂The solution was precipitated from the insulin containing fraction at pH 6.8. The insulin was filtered off and then dissolved in 0.05M Tris-HCl (pH 8.5) to give a 2mg/ml solution.

About 1 unit of carboxypeptidase B is then added to each 100ml of solution and the reaction is allowed to proceed with gentle agitation. Then adjusting the pH to 5.5 with citric acid and adding insulin to ZnCl₂Crystallizing in the presence of. The crystals are removed, dissolved and purified by RP-HPLC, and the insulin is purified by crystallization.

Example 9: direct processing of fusion proteins in culture media

At the end of the expression phase, the medium was adjusted to pH 6.8 and then trypsin was added with stirring to 4-8mg per liter. After an incubation time of about 4 hours, the fermentation broth treated in this way is adjusted to a pH of 2.5 to 3. After 1-6 hours of precipitation, the pH was raised to 3.5 and the formed bis-Arg-insulin was purified by cation exchange chromatography in the presence of 30% 2-propanol. Elution was performed by a gradient of NaCl from 0.05 to 0.5M. The product-containing fractions are diluted 1: 1 with water and ZnCl is subsequently added₂So that it forms ZnCl of 0.1% strength₂And (3) solution. bis-Arg-insulin precipitates at pH 6.8 and can then be determined, for example, byExample 8 conversion to insulin.

Example 10: additional Signal sequences for secretion of fusion proteins

Other signal sequences which lead to the secretion of the hirudin-proinsulin fusion protein can be detected by the technique described in patent application PCT/EP 00/08537:

signal sequence smompaFrom the ompA gene of the major outer membrane protein of Serratia marcescens (Serratia marcocens) (GenEMBL database location: SMOMPA, 1364bpDNA BCT 30-3-1995)

Signal sequence ecoompcDerived from the ompC gene of E.coli encoding the major outer membrane protein (GenEMBL database location: SMOMPA, 1364bp, DNA BCT 30-3-1995)

Signal sequence af009352Derived from the Bacillus subtilis osmoprotectants binding protein precursor (opuCC) (GenEMBL database mapping: AF009532, 4500bp, DNA BCT 23-7-1997)

Signal sequence aexynaFrom Aeromonas caviae (Aeromonas caviae) encoding xylanase I precursor xynA gene (GenEMBL database location: AEOXYNA, 1139bp, DNA BCT 07-2-1999)

Signal sequence moments 1Derived from the gene of Salmonella typhimurium (S.typhi) encoding the outer membrane protein S1 (GenEMBL database location: STOMPS1, 1938bp, DNA BCT24-8-1995)

Sequence listing

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<223> description of artificial sequences: alkaline phosphatase (Signal sequence)

<400>7

Met Lys Gln Ser Thr Ile Ala Leu Ala Leu Leu Pro Leu Leu Phe Thr

1 5 10 15

Pro Val Thr Lys Ala

20

<210>8

<211>63

<212>DNA

<213> Artificial sequence

<220>

<400>8

atgaaacagt cgaccatcgc gctggcgctg ctgccgctgc tgttcacccc ggttaccaaa 60

gcg 63

<210>9

<211>97

<212>DNA

<213> Artificial sequence

<220>

<223> description of artificial sequences: cloning of fragments

<400>9

ttttttgaat tcatgaaaca gtcgaccatc gcgctggcgc tgctgccgct gctgttcacc 60

ccggttacca aagcggctac gtatactgac tgcactg 97

<210>10

<211>58

<212>DNA

<213> Artificial sequence

<220>

<223> description of artificial sequences: phoaf1

<400>10

ctgctgccgc tgctgttcac cccggttacc aaagcggcta cgtatactga ctgcactg 58

<210>11

<211>54

<212>DNA

<213> Artificial sequence

<220>

<223> description of artificial sequences: phoaf2

<400>11

ttttttgaat tcatgaaaca gtcgaccatc gcgctggcgc tgctgccgct gctg 54

<210>12

<211>40

<212>DNA

<213> Artificial sequence

<220>

<223> description of artificial sequences: hir _ inst 2

<400>12

atccc tgagg aataccttca gcgat t tgtg aaccagcacc 40

<210>13

<211>40

<212>DNA

<213> Artificial sequence

<220>

<223> description of artificial sequences: hir _ instrev 2

<400>13

ggtgctggtt cacaaatcgc tgaaggtatt cctcagggat 40

Claims

1. DNA encoding fusion protein having-F-As_m-R_n-the form-Y-is,

wherein,

m is an integer of 0 to 10,

r is a chemical bond or an arginine codon,

n is 0 or 1, and

y is a DNA sequence encoding a protein of interest which is correctly folded in the fermentation medium and is part of a fusion protein.

2. The DNA of claim 1, wherein the expression cassette is P-S-F-As_m-R_nform-Y-T, wherein

P is a promoter

S is a DNA sequence encoding a signal sequence which leads to an optimal yield,

t is an untranslated DNA sequence which can enhance expression.

3. The DNA of claim 2, wherein S is: the oprF gene derived from Pseudomonas fluorescens; a DNA encoding a signal sequence of Salmonella typhimurium outer membrane protein (fim D); a DNA sequence encoding a signal sequence of an E.coli alkaline phosphatase precursor protein; a DNA sequence encoding a signal sequence smompa derived from the ompA gene of serratia marcescens encoding a major outer membrane protein; a DNA sequence encoding a signal sequence ecoampc derived from the ompC gene of E.coli encoding a major outer membrane protein; a DNA sequence encoding a signal sequence af009352, said signal sequence af009352 being derived from the bacillus subtilis osmoprotectantt binding protein precursor (opuCC); a DNA sequence encoding a signal sequence aexyna derived from the xynA gene of Aeromonas caviae encoding a xylanase I precursor; or a DNA sequence encoding a signal sequence moments 1, said signal sequence moments 1 being derived from the gene encoding the outer membrane protein S1 of Salmonella typhimurium.

4. DNA according to any one of claims 2 or 3, in which the DNA sequence F is lepirudin, Ser-hirudin or Ala-hirudin.

5. The DNA according to any one of claims 2 to 4, wherein the protein of interest Y is proinsulin, insulin or a derivative thereof.

6. A protein encoded by the DNA according to any one of claims 1 to 5.

7. A plasmid containing the DNA according to any one of claims 1 to 5.

8. A host cell comprising the plasmid of claim 7.

9. A host cell comprising the DNA of any one of claims 1 to 5.

10. The host cell according to claim 8 or 9, wherein the cell is selected from the group consisting of escherichia coli, bacillus subtilis and streptomyces, and the plasmid according to claim 7 and the DNA according to any one of claims 1 to 5 are optionally integrated into the genome of the host cell.

11. Method for the fermentative production of fusion proteins, in which method

(a) The DNA molecule of any one of claims 1 to 5 expressed in a host cell of any one of claims 8 to 10; and is

(b) The expressed fusion protein was isolated.

12. The method of claim 11, wherein the supernatant is separated from the host cell to isolate the expressed protein, and the expressed protein is then separated from the supernatant.

13. The method according to any one of claims 11 or 12, wherein the step for concentrating the expressed protein in the supernatant after precipitation is selected from the group consisting of microfiltration, hydrophobic interaction chromatography and ion exchange chromatography.

14. The method according to any one of claims 11 to 13, wherein the isolation of the expressed protein comprises the steps of: the components in the medium or supernatant are precipitated to keep the expressed protein in solution.

15. The process according to any one of claims 11 to 14, wherein after fermentation, thiol or cysteine hydrochloride is added to the fermentation supernatant at a pH of 6-9, resulting in a concentration of free SH groups of 0.05 to 2.5 mM.

16. The process according to any one of claims 11 to 15, wherein after separation of the fermentation supernatant from the host cells, the host cells are repeatedly cultured in fresh medium and the released fusion protein is separated from each supernatant obtained in the culture.

17. The method according to any one of claims 11 to 15, wherein the thiol or cysteine hydrochloride is added to the supernatant of the cell culture at a pH of 6-9 to bring the concentration of free SH groups to 0.05 to 2.5 mM.

18. A process for the production of insulin or an insulin derivative, wherein

a) The protein expressed by the method according to any one of claims 11 to 17,

b) liberating the protein of interest, in particular insulin or an insulin derivative, by enzymatic or chemical cleavage, and

c) it is isolated.